The invention is based on a valve for regulating fluids.
One such valve is described, in German Patent Disclosure DE 197 328 02, for a fuel injection device of an internal combustion engine having a high-pressure system (common rail system). This fuel injection device has two valve seats, which cooperate with sealing faces of a valve closing member upon actuation by a piezoelectric drive in a sequence of motion, in which the valve closing member is initially in the closing position on the first valve seat, then is moved into an intermediate position between the valve seats, and then returns to a closing position against the second valve seat. To that end, a piezoelectric actuator is charged to a rail-pressure-dependent voltage, which causes an elongation of the actuator and a resultant motion of the valve closing member toward the second valve seat. For the reversing motion of the valve closing member in the direction of the first valve seat, the actuator is discharged again.
By the course of motion of the valve closing member from one valve seat to the other, a brief relief of a valve control chamber, which is under high pressure, is attained; by way of its pressure level, an opening and closing position of a valve needle is determined in the fuel injection device, which is embodied in force-balanced fashion, and the fuel injection is thus controlled. The fuel injection is enabled while the valve closing member is in an intermediate position between the two valve seats. In this way, even a double fuel injection, such as a pre-injection and a main injection, can be achieved by means of a single excitation of the piezoelectric drive.
Since the triggering of the valve member is done not directly but rather by means of a hydraulic booster, the pressure buildup in the hydraulic chamber, functioning as a hydraulic coupler, is decisive for the length of the stroke of the valve member. If the piezoelectric actuator is subjected to such high voltage that the valve closing member moves out of its valve seat, then some of the fuel quantity located in the hydraulic chamber is forced out via the leakage gaps from this chamber. This effect is especially pronounced if the control valve is held on the second valve seat, toward the high-pressure region, since in that case the counterpart force from the rail pressure is especially strong. The refilling of the low-pressure region or of the hydraulic coupler is done by means of a system pressure, which in practice can for instance amount to 15 bar, once again via these leakage gaps, but in this case only during the time while the piezoelectric actuator is not triggered.
The same is true for similar valves known from practice, which are equipped with only one valve seat and in which the valve closing member is lifted out of this valve seat and moved back again.
In all these valves, when injections occur in quick succession, the problem exists that the hydraulic coupler is as a rule not completely refilled. The valve stroke that is set with the same trigger voltage of the piezoelectric actuator and thus the same actuator stroke in these injections therefore varies. The closer together two injections occur, that is, the shorter the refill time between injections is, and the longer the actuator was previously triggered or in other words the greater the loading time of the hydraulic coupler and thus the greater the leakage quantity, the more marked is the adverse effect described. The variable actuator stroke in turn disadvantageously causes inaccuracies in metering the injection quantity; under some circumstances, the actuator stroke can be so short that it has no effect on the valve needle, and in the case involving use as a fuel injection valve, no fuel injection for instance occurs.
The valve of the invention for regulating fluids, has the advantage that the valve stroke that is set can be executed identically for all injections, by means of a suitably modified trigger voltage of the piezoelectric unit. It is thus possible, even at a high prevailing pressure level in the high-pressure region, to execute injections in quick succession, as may be necessary in a pre-injection, main injection and post-injection to improve the fuel consumption and emissions values, with a replicable stroke length for all the injections, since the varying fill level of the low-pressure region or of the hydraulic coupler, which is represented by the hydraulic chamber, can be compensated for by way of the trigger voltage.
With the valve of the invention, in which in addition to taking the pressure level in the high-pressure region into account, a modification of the trigger voltage is done as a function of leakage losses and refilling, a stable injection can advantageously be guaranteed.
In an especially advantageous version of the invention, it can be provided that to ascertain the leakage loss from the low-pressure region, a triggering duration of a preceding injection is output to the electric trigger unit. The triggering duration of the preceding injection represents a reliable variable for the quantity of hydraulic fluid that was expelled through leakage points during the loading time of the hydraulic coupler.
In a further advantageous version of the valve of the invention, it can provided that a time interval between an end of the preceding injection and the onset of the next injection is output to the electric control unit as a highly reliable value for the refilling of the low-pressure region, because this time interval as a rule does correspond to the refilling time. The fill factor of the coupler before the next injection can thus be determined from the refill time and the loading time.
Further advantages and advantageous features of the subject of the invention can be learned from the specification, drawing and claims.